New trends in the architectural design of footbridges feature an unprecedented slenderness, especially when these are located in the urban environment. For this reason, static analyses and a design towards the ultimate limit state have proven inadequate in many circumstances, and the main objective in the structural design is becoming that of assessing the serviceability limit state through dynamic analyses. On the other hand, the key issue of dynamic analyses is the availability of reliable models for the structure and for loads, and in the particular case of pedestrian action the lack of commonly accepted models for walking, running and jumping has become the weak link in the whole structural design process. In a first stage of the present work, vibration measurements were taken on a recently built cable-stayed footbridge, whose second vibration mode was excited by runners. As a second step, a dynamic loading model for the vertical component of the running-induced force was developed, which was used for the finite element analyses of the footbridge. Finally, tuned mass dampers (TMDs) represent a quite mature technology for reducing the resonant response of flexible structures, but their effectiveness is heavily dependent on the tuning ratio. In the case of footbridges, pedestrians can act as a significant part of the vibrating mass; thus, varying the vibration frequency, which makes it difficult to properly tune the damper frequency. Semi-active TMDs can be looked at as passive devices able to adjust their dynamic parameters according to a given control logic. A physical description of a control algorithm is given in the paper, and its performance is discussed.

The possibility of reducing structural response under strong external excitations such as earthquakes and wind storms via control systems is attracting the interest of a large number of researchers. In the field of civil structures, control systems based on semi-active devices seem to be close to feasible implementation. Semi-active devices are typically passive elements capable of self-adjusting their own mechanical properties according to the instantaneous response of the hosting structure and, therefore, they can be considered as smart devices. Even though dampers based on magnetorheological fluids are considered very effective in practical implementations, the literature examining their properties from the structural control point of view is still quite limited. This paper aims to show the potential of such devices and to describe their properties from this special perspective. These properties include manufacturing issues, powering, range of variability of the mechanical parameters, their dependence on the feed current and overall response time.

This paper details the findings of an experimental program that assessed the seismic performances of a novel low-cost base isolation device. The proposed bearings are referred to as recycled rubber-fiber-reinforced bearings (RR-FRBs). Devices composed of a low-cost recycled elastomer and reinforced with fiber sheets were manufactured and tested.The main revolutionary concepts investigated in this study are as follows: low-performance elastomers can be used to produce rubber isolators, and vulcanization can be prevented by bonding different layers with an elastic compound.This study addresses all design and technical aspects related to the implementation of the proposed base isolation system. Shaking table tests showed a significant improvement in the seismic performance of an RR-FRB isolated building with respect to a corresponding fixed-base structure.All peak measured quantities for the seven input earthquakes are listed in Table II. The table also shows the peak response of the corresponding 5% damped fixed-base structure. The structure, which was fixed at the base, did not yield during the seismic events. The measurements listed in the table indicate adequate capacity of the proposed technology in reducing the seismic demand on the structure.The response reductions in terms of interstory drift and top floor acceleration for each ground motion are shown in Figure 6. For the seven records, an average reduction of 55% was measured for the roof acceleration (i.e., columns shear), whereas an average reduction of 33% was determined for the interstory drift. The tests indicated different performances of the bearings with increasing energy content of the seismic events at the isolator's frequency. For instance, for both Campania records (CAM and CAT), significant reduction in the top floor acceleration (almost 60%) was observed. Figure 9. Amplification envelopes: isolated building versus 5% damped structure. RECYCLED RUBBER-FIBER-REINFORCED BEARINGS

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